This is the renewal of research project NS-09871, entitled Neuropharmacology-Anesthesia and the Nervous System. The research projects proposed herein are extensions of the previous studies but with considerable departure from past approaches, and are aimed at the study of the activity of sensory neurons, modulated by anesthetics and analgesics, at three levels of the central nervous system while physiological parameters are strictly maintained within the normal range. The departure from past approaches defined below shows our new direction. It is proposed to study the pharmacologic effects of anesthesia utilizing microelectrode recording techniques with the aid of a computerized statistical data analysis program available in our laboratory, at the Dorsal horn of spinal cord, the subnucleus caudalis of the trigeminal system and the nucleus reticularis gigantocellularis of the pontomedullary reticular formation areas known to transmit nociciptive information. The study is aimed at the comparison of the data in these three areas in order to clarify the major sites and modes of action of the production of analgesia by the agents studied, to investigate the interaction among the nuclear groups, and to test our hypothesis that anesthetics have a preferential depressant effect upon the "central nociceptors" while leaving the activity of other neurons relatively unaffected. To simulate surgical stimuli, a thermal stimulus will be used, which is controllable, reproducible, conveniently applied and causes minimal tissue damage.